When challenged with inhibitors of steroidogenesis, the cultured vascular smooth muscle cell showed depressed synthesis of cholesterol and of dolichyl (pyro) phosphate and an accompanying loss of cellular cholesterol. It was deduced that a regulatory site for the synthesis of both substances might occur at the HMG-Coa reductase. As a consequence of this inhibition cellular glycoprotein synthesis was diminished, and it was concluded that the availability of dolichyl(pyro)phosphates which mediate glycoprotein synthesis may also contribute to the regulation of their assembly. Cellular response to these changes may involve redistribution of subcellular membrane systems. This redistribution, perhaps necessary as a defense response, may present the cell with a new set of problems. Such redistribution will be assessed in a variety of conditions using subcellular fractionation schemes and marker enzymes assays. It is now clear that loss of cellular cholesterol may also contribute to defective glycoprotein assembly and membrane biogenesis. Such an effect points to the importance of a metabolically active cholesterol pool which the cell synthesizes to make certain that proper assembly is maintained. In view of this, contribution of exogenous cholesterol, supplied in a variety of forms, to such a pool will also be investigated.